In recent years, the research and development have been rapidly proceeded for an optical pick-up device, which is capable of recording and/or reproducing information by means of a high-density optical disk (hereinafter, “recording and/or reproducing” will be expressed by using following wording “recording/reproducing”) by using a blue-violet semiconductor laser having wavelength of about 400 nm and the optical pick-up device is already on the market. As an example of the high-density optical disk, regarding so-called a “Blu-ray Disc” (hereinafter it will be called BD) which conducts recording/reproducing of information with the specification of NA 0.85 and wavelength of a light source equal to 405 nm, information of 25 GB per a layer can be recorded on the optical disk having a diameter of 12 cm, which is the same size as a DVD (NA 0.6 and wavelength of a light source 650 nm and recording capacity 4.7 GB).
On the other hand, it is sometimes considered that a product, such as an optical disk player/recorder (optical information record reproducing device), which is capable of only recording/reproducing information for the above type of high-density optical disk is not valuable enough. Taking account of a fact that, at present, DVDs and CDs (Compact Disk), onto which various kinds of information have been recorded, are on the market, the value of the product as a high-density optical disk player/recorder is increased by, not only enabling to record/reproduce information for the high-density optical disk, for example, but also enabling to appropriately record/reproduce information additionally for DVDs and CDs, which a user possesses. From these backgrounds, the optical pick-up device installed in the high-density optical disk player/recorder is required to be capable of appropriately recording/reproducing information for anyone of high-density optical disk, a DVD and a CD while keeping compatibility.
It can be considered, as a method by which the information can be adequately recorded/reproduced while the compatibility is maintained also to anyone of the high density optical disk and DVD and further to CD, a method to selectively switch an optical system for the high density optical disk and an optical system for DVD and CD corresponding to the recording density of the optical disk to which the information is recorded/reproduced. However, it requires a plurality of optical systems, which is disadvantageous for the size-reduction and which increases the cost.
Accordingly, in order to simplify the structure of the optical pick-up device and to intend the reduction of cost, it is preferable to make an optical system for the high density optical disk and an optical system for DVD and CD into a common optical system, and to reduce the number of optical parts contributing the optical pick-up device as much as possible, even when the optical pick-up device has compatibility. Then, providing an objective optical element which is arranged to face an optical disk in common as much as possible, is most advantageous for the size-reduction of the construction or cost reduction of the optical pick-up device.
Concerning the above, Patent Document 1 describes an optical pick-up device which, using a common objective lens, focuses light beams having three different wavelengths onto the information recording surfaces of a high density optical disk, DVD, and CD, and carries out recording and/or reproducing of information compatibly with them.